Filler caps or fuel caps, such as for fuel tanks of airplanes, seal an adapter member which defines the opening of the tank. Typically, these caps must be constructed to meet rigid specifications and standards set forth by various governmental or regulatory agencies. For example, according to one military standard (MIL-C-38373B) by the Department of the Air Force and the Naval Air System Command, the fuel cap must be lightning safe, fuel resistant, and sufficiently resilient to be subjected to withstand a burst pressure of 100 psi for one minute without distortion or other injury.
Various fuel caps have been designed for meeting the different specifications and standards. Typically, these fuel caps are constructed with a plug member for effecting a seal with the tank opening and a cooperating locking mechanism for locking the cap onto the tank in a sealed position. Particularly, the sealing of the plug member against the annular wall of the adapter member is effected by an O-ring positioned in a groove about the periphery of the plug member. See, for example, U.S. Pat. No. 3,391,817. As the cap is lowered into the tank opening, the sealing member or O-ring is deformed into positive engagement with the annular wall of the adapter member, creating a tight circumferential seal. In some instances, however, the O-ring is deformed radially outward by the internal pressure or fuel-induced swelling, inhibiting pressure relief or decompression when the cap is unlocked.
One alternative for reliably relieving the internal pressure in the tank without interference from the sealing member is described in U.S. Pat. No. 4,189,059. This patent discloses a fuel cap comprising a plug member having an outwardly extending flange at its upper end and a lower end having a contact surface for contacting a sealing member disposed about the plug periphery, and a retaining member positioned below the sealing member for compressing the sealing member against the lower end of the plug member. The surface of the lower end of the plug member, and the upper surface of the retaining member define between them a first grooved portion for clinching the sealing member in position adjacent to the plug periphery and a second radially inwardly disposed grooved portion of reduced cross section for accommodating fuel induced swelling. Advantageously, with the clinch groove restraining radially the sealing member from outward deformation and the accommodation groove receiving the deformation radially inward, the fuel cap is able to relieve pressure without interference from the sealing member.
Further, it would also be highly desirable to have a fuel cap which can reliably relieve internal tank pressures at elevated pressures while still minimizing the deleterious effects of fuel or temperature induced swelling.